Thermally insulated suspension load beam
A suspension load beam for use in supporting a transducer head in a data storage system includes a front beam section, a rear beam section, and a middle beam section. The front beam section is configured to connect to a slider assembly carrying a transducer head. The rear beam section is configured to connect to an actuator arm. The middle beam section is located between the front beam section and the rear beam section. The middle beam section comprises a top thermal insulation layer, a bottom thermal insulation layer and a rigid layer between the top and bottom thermal insulation layers.
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The present invention relates to a suspension load beam configured to carry a transducer head. More particularly, the present invention relates to a suspension load beam having thermal insulation layers that reduce structural distortion of the suspension load beam in response to environmental temperature changes.
Disc drives are data storage devices that store digital data in magnetic form on a rotating disc. Modern disc drives comprise one or more rigid information storage discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation. Data is read from and written to a plurality of concentric circular tracks on the discs by transducer heads (“read/write heads”) that are carried by sliders placed in close proximity to the disc surfaces. Each slider is attached through a gimbal system to a distal end of a suspension load beam. The proximal end of the suspension load beam is attached to an actuator arm that rotates to move the slider to a desired position relative to the associated disc surface.
During a write operation sequential data is written onto the disc track, and during a read operation the head senses the data previously written onto the disc track and transfers the information to an external environment. Important to both of these operations is the accurate and efficient positioning of the head relative to the center of the desired track on the disc (i.e., track following).
Head positioning within a desired track is dependent on head-positioning servo patterns, which are patterns of data bits recorded on the disc surface that are used to maintain optimum track spacing and sector timing. The servo patterns or information can be located between the data sectors on each track of a disc (“embedded servo”), or on only one surface of one of the discs within the disc drive (“dedicated servo”).
The servo patterns are typically recorded on the magnetizable medium of a target disc by a servo-track writer (“STW”) assembly during the manufacture of the disc drive. One type of STW assembly records servo pattern on the discs following assembly of the disc drive. The STW assembly attaches directly to a disc drive having a disc pack where the mounted discs on the disc pack have not been pre-recorded with servo pattern. The STW essentially uses the drive's own read/write heads to record the requisite servo pattern directly to the mounted discs. An alternative method for servo pattern recording utilizes a separate STW assembly having dedicated servo recording transducers or heads for recording servo pattern onto one or more discs. The dedicated servo recording heads can be used to record servo information to a number of discs simultaneously, which are subsequently loaded into the disc drive for use.
Recent efforts within the disc drive industry have focused on developing cost-effective disc drives capable of storing more data onto existing or smaller-sized discs. One potential way of increasing data storage on a disc surface is to increase the recording density of the magnetizable medium by increasing the track density (i.e., the number of tracks per inch). Increased track density requires more closely-spaced, narrow tracks and therefore enhanced accuracy in the recording of the servo-patterns onto the target disc surface.
Thermal distortion of the suspension load beam can contribute to errors in the positioning of the servo-patterns relative to the target disc. The principle of thermal expansion states that essentially all solids expand in volume when the temperature is raised. When the temperature is increased, the average distance between atoms increases, which leads to an expansion of the whole solid body.
During disc drive or STW operation, temperature gradients in the suspension load beam continuously change over time. These changes are due in part to varying wind currents around the suspension load beam and the varying heat contributions of components of the device. The resultant thermal distortions to the structure of the suspension load beam cause the position of the transducer head to deviate from the desired position, which affects the accuracy at which the servo-patterns can be written. As a result, such thermal distortions can limit the track density of the recording medium and can introduce undesirable repeatable runout that must be compensated for by the disc drive during track following (e.g., data read and write operations).
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages.
SUMMARYThe present invention generally relates to a suspension load beam for use in supporting a transducer head in a data storage system. In one embodiment, the suspension load beam includes a front beam section, a rear beam section, and a middle beam section. The front beam section is configured to connect to a slider assembly carrying a transducer head. The rear beam section is configured to connect to an actuator arm. The middle beam section is located between the front beam section and the rear beam section. The middle beam section comprises a top thermal insulation layer, a bottom thermal insulation layer and a rigid layer between the top and bottom thermal insulation layers.
Other features and benefits that characterize embodiments of the present invention will be apparent upon reading the following detailed description and review of the associated drawings.
The environmental temperature within the disc drive 120 or STW 160 constantly changes during operation. The changing temperature is due, in part, to the many heat generating components of the disc drive 120 or STW 160, such as, for example, preamplifiers, the spindle hub, etc. The generated heat is transferred to the suspension load beam 100 through conduction, such as through the connected actuator arm (134, 174), and convection.
The continuously changing environmental temperature that suspension load beam 100 of disc drives and STW's are subjected to produce time-varying temperature gradients in the suspension load beams. The changes in the temperature gradients within the suspension load beams lead to non-uniform expansion and contraction of the structures. As a result, the suspension load beams undergo structural distortions during operation that results in a change in the position and/or orientation of the front beam sections and, thus, the supported transducer heads, even when the actuator arms are held in a fixed position.
During servo-pattern writing operations, the precise position of the heads of the disc drive or the STW is unknown. As a result, an estimate of the position of the heads must be made using conventional techniques, such as with a laser interferometer, that detects a position of the actuator arms to which the heads are attached through suspension load beams. Although conventional head positioning techniques are highly accurate, they cannot take into account the low frequency head movement caused by the thermal distortion of the suspension load beams. Accordingly, such thermally induced movement of the transducer head affects the accuracy at which servo-patterns can be written and, thus, limits the track density of the recording disc. Additionally, the thermally induced motion of the transducer head also produces non-repeatable runout that must be compensated for by the servo electronics of the disc drive in order to follow a desired track during a data reading or writing operation.
The suspension load beam 100 of the present invention is useful in improving the accuracy of the positioning of the transducer heads 113 during use in disc drives 120 or STW's 160 by reducing the sensitivity of the suspension load beam 100 to environmental temperature changes. In particular, the suspension load beam 100 is thermally isolated from the temperature fluctuations of the operating environment to thereby reduce the fluctuations in the temperature gradients within the suspension load beam 100. As a result, the suspension load beam 100 has a lower sensitivity to temperature fluctuations, which reduces thermally induced low frequency movement of the attached transducer head 113 and leads to more accurate head positioning.
One measure of a structure's sensitivity to distortion from changing environmental temperatures is the thermal time constant. In general, the lower the thermal time constant, the faster the beam responds to environmental temperature changes.
The thermal time constant of a rectangular beam formed of a single material and having similar dimensions as the suspension load beam of
Embodiments of the suspension load beam 100 include top and bottom thermal insulation layers 180 and 182 respectively on top and bottom sides 184 and 186 of a rigid layer 188, as illustrated in the cross-sectional view of
The thermal insulation layers 180 and 182 of the beam 100 of the present invention operate to raise the thermal time constant of the suspension load beam 100 and reduce its sensitivity to temperature fluctuations in the operating environment, as compared to a suspension load beam formed solely from the rigid layer 188 (i.e., lacking the thermal insulation layers). The effective time-constant (τeff) of the suspension load beam 100 of the present invention (
In Eq. 2, t1 is the thickness of the rigid layer 188, t2 is the thickness of the thermal insulation layer 180, t3 is the thickness of the thermal insulation layer 182, ρ1 is the density of the rigid layer 188, ρ2 is the density of the thermal insulation layer 180, ρ3 is the density of the thermal insulation layer 182, Cp1 is the specific heat capacity of the rigid layer 188, Cp2 is the specific heat capacity of the thermal insulation layer 180, Cp3 is the specific heat capacity of the thermal insulation layer 182, Vtot is the total volume of the suspension load beam 100 and As is the heat transfer surface area of the load beam 100.
Suspension load beams formed solely from a stainless steel rigid layer 188 (i.e., lacking the thermal insulation layers 180 and 182) are highly susceptible to thermally induced structural distortion caused by fluctuating temperature gradients within the structure due to a low thermal time constant. For example, the time constant for the suspension load beam of
However, when the above suspension load beam formed solely of the stainless steel rigid layer 188 is sandwiched between thermal insulation layers 180 and 182 in accordance with embodiments of the invention, the effective time constant can be increased significantly. This is demonstrated in Table 1, which provides a comparison between exemplary suspension load beams of the present invention having insulation layers 180 and 182 formed from various materials. The exemplary load beam 100 includes a unitary rigid layer 188 of stainless steel that forms the rear beam section 106, the middle beam section 104 and the front beam section 102, and has a thickness (t1) of 2.4 mils, a density (ρ1) of 7800 kg/m3 and a specific heat capacity (Cp1) of 500 J/(kgK). The insulation layers 180 and 182 of the exemplary load beam 100 each have a thickness (t2 and t3) of 1 mil. The density (ρ2 and ρ3) and specific heat capacity (Cp2 and Cp3) is given for the particular material used to form the insulation layers 180 and 182. Table 1 also lists the time constant of the rigid layer 188 (τ1), the time constant of each of the thermal insulation layers 180 and 182 (τ2 and τ3), the effective specific heat capacity (Cpeff) of the beam 100, the effective time constant of the beam 100 (τeff) and the ratio of the effective time constant to the time constant of a beam formed solely from the rigid layer 188 (τeff/τ1).
As shown in Table 1, the various exemplary insulation layers 180 and 182 increase the effective time constant of the exemplary suspension load beam 106 by 50 to 100 percent over that of the beam formed solely of the stainless steel rigid layer 188. As a result, the exemplary beam 100 will respond at least 1.5 times slower to changes in its thermal environment. In one embodiment, the insulation layer materials and thicknesses are selected to provide at least a 40 percent increase in the time constant.
Accordingly, the suspension load beam 100 of the present invention will have a lower time-varying deflection of a transducer head 113 supported at the front beam section 102 resulting in more accurate positioning of the head 113. Accordingly, the use of the suspension load beam 100 in an STW 160 or a disc drive 120 can improve its recording density capability. Additionally, the suspension load beam 100 of the present invention can also reduce thermally induced non-repeatable runout during track following operations.
Embodiments of the suspension load beam 100 include the use of the materials of Table 1 to form the insulation layers 180 and 182, as well as other suitable insulation materials. The important properties of the thermal insulation layers 180 and 182 that would increase the effective time constant and thus better isolate the beam 100 from environmental thermal fluctuations include high specific heat capacity, high density and large thickness. Embodiments of the suspension load beam 100 include the formation of the insulation layers using the same or different materials.
In one embodiment the rigid layer 188 is unitary and forms the main structure of the front beam section 102, the middle beam section 104 and the rear beam section 106. Alternatively, the rigid layer 188 forms at least one of the front beam section 102, the middle beam section 104 and the rear beam section 106. The rigid layer 188 can be formed of stainless steel, plastic or other suitable material. Alternatively, the rigid layer 188 can comprise a laminated structure.
Embodiments of the suspension load beam 100 include the application of the insulation layers 180 and 182 to the front beam section 102 (
In another embodiment, the thermal insulation layers 180 and 182 are applied over select portions of the surfaces 184 and 186 of the rigid layer 188. Thus, where the rigid layer 188 is a unitary member that forms the front beam section 102, the middle beam section 104 and the rear beam section 106, the insulation layers 180 and 182 may be applied only to select portions of one or more of the various sections. Accordingly, embodiments of the load beam include the insulation layers 180 and 182 on select surfaces of the front beam section 102, the middle beam section 104 and/or the rear beam section 106.
The thicknesses of the insulation layers 180 and 182 can be the same or different. The thickness and choice of materials for the thermal insulation layers can be selected to best suit the desired application and provide the desired time constant increase. Embodiments of the insulation layers include thicknesses (t2 and t3) of greater than 0.3 mils. Other desirable properties of the thermal insulation layers include low thermal conductivity and good adhesion to the surfaces of the rigid layer.
Additional embodiments of the invention include various methods for applying the thermal insulation layers 180 and 182 to the rigid layer 188.
The particular technique of bonding or applying the insulation layers 180 and 182 to the rigid layer 188 (steps 202 and 204) can depend on the material used to form the insulation layers. In one embodiment, a coating technique is used to bond or apply the insulative materials to the rigid layer 188 and form the insulation layers 180 and 182. Exemplary coating techniques include spray coating, plasma coating, and dip coating.
In another embodiment, the insulation layers 180 and 182 are applied or bonded to the rigid layer using a deposition technique, such as a physical vapor deposition or other deposition technique.
Surfaces of the rigid layer 188 on which the insulation layers are not desired can be masked off in accordance with conventional methods.
It is to be understood that even though numerous characteristics and advantages of various embodiments of the invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements used to form the suspension load beam may vary depending on the particular application for the suspension load beam while maintaining substantially the same functionality without departing from the scope and spirit of the present invention.
Claims
1. A suspension load beam comprising:
- a front beam section defining a mounting feature for connecting to a data transfer member at a distal end of the suspension load beam;
- a rear beam section defining another mounting feature for connecting to a support structure at a proximal end of the suspension load beam; and
- a middle beam section extending between and contiguous with both the front beam section and the rear beam section, wherein the middle beam section comprises a rigid layer sandwiched between opposing thermal insulation layers, wherein each thermal insulation layer has a first surface that contactingly engages a respective surface of the rigid layer throughout the entire middle beam section, and each thermal insulation layer has an opposing second surface that defines an exposed external surface of the suspension load beam covering the rigid layer surface throughout the entire middle beam section.
2. The suspension load beam of claim 1, wherein the front beam section is unitary with the rigid layer of the middle beam section.
3. The suspension load beam of claim 2, wherein the front beam section is sandwiched between the opposing thermal insulation layers.
4. The suspension load beam of claim 1, wherein the rear beam section is unitary with the rigid layer of the middle beam section.
5. The suspension load beam of claim 4, wherein the rear beam section is sandwiched between the opposing thermal insulation layers.
6. The suspension load beam of claim 1, wherein the rigid layer comprises a stainless steel sheet material.
7. The suspension load beam of claim 1, wherein a thermal time constant of the suspension load beam is substantially higher than a thermal time constant of just the rigid layer.
8. A method for fabricating a thermally insulated suspension load beam, the method comprising:
- obtaining a rigid layer comprising: a front beam section defining a mounting feature for connecting to a data transfer member at a distal end of the thermally insulated suspension load beam; a rear beam section defining another mounting feature for connecting to a support structure at a proximal end of the thermally insulated suspension load beam; and a middle beam section extending between and contiguous to both the front beam section and the rear beam section;
- bonding opposing thermal insulation layers to the rigid layer, wherein each thermal insulation layer has a first surface that contactingly engages a respective surface of the rigid layer throughout the entire middle beam section, and each thermal insulation layer has an opposing second surface that defines an exposed external surface of the suspension load beam covering the rigid layer surface throughout the entire middle beam section.
9. The method of claim 8, including setting a thickness of each of the opposing thermal insulation layers such that a thermal time constant of the suspension load beam is substantially higher than a thermal time constant of just the rigid layer.
Type: Grant
Filed: Jan 10, 2006
Date of Patent: Mar 12, 2013
Patent Publication Number: 20070159725
Assignee: Seagate Technology LLC (Cupertino, CA)
Inventor: Krishna Prashanth Anandan (Edina, MN)
Primary Examiner: Will J Klimowicz
Application Number: 11/328,556